New cochlear implant could improve hearing

A ribbon-like cochlear implant developed at the University could improve hearing for profoundly deaf patients and simplify insertion to help surgeons minimize damage to healthy ear tissue.

(Photo courtesy Kensall Wise Lab)

A team led by Kensall Wise, director of the NSF Engineering Research Center for Wireless Integrated Microsystems, made the implant using thin-film electrode sites that directly stimulate the auditory nerve.

The implant currently is being tested in guinea pigs and cats, says Wise, who has appointments in the departments of Biomedical Engineering, and Electrical Engineering and Computer Science. The device may be available in 4-5 years for use in humans and could be used in current cochlear patients to improve hearing. Additionally, the FDA approves implants for wider use as the technology improves.

Approximately 100,000 patients worldwide have received cochlear implants. The current technology, Wise says, is bulky, difficult for surgeons to insert and doesn't allow a great range of perceived frequencies. The implants use electrodes formed from a bundle of wires fed into the snail-shaped cochlea of the inner ear, but difficulties inserting such devices make it tough to achieve the depth needed to stimulate lower-frequency sounds, Wise says, and collisions with the cochlear wall can damage any residual hearing.

"The range of frequencies that can be stimulated depends on how far into the cochlea the implant can go, with the lower frequencies located further up toward the apex of the spiral canal," Wise says. In current technology, each implant has anywhere from 16-22 stimulating sites along its length. By contrast, the U-M implant will host up to 128 stimulating sites.

The ribbon film technology enables researchers to embed other functions in the implant, such as position sensors that allow surgeons to watch the implant's progress on a monitor as they're feeding it into the cochlea.

"Eventually the idea is to be able take the signals from the position sensors and use them to control actuators in an insertion tool, so that the electrode array can achieve deep insertion and navigate around any obstacles in its path," Wise says.

"The idea is to use a pneumatic insertion tool that can be inflated or deflated, similar to a spiral party favor, and is pre-stressed to hug the inner wall of the cochlea," Wise says. "The position sensors set the stage for doing that because they give you feedback on what's happening when you insert these devices."

Researchers make the implant with the same processes used to make integrated circuits, which means they can be made in batch.

The research, funded by the National Science Foundation, was presented Feb. 6 at the International Solid-State Circuits Conference in San Francisco. Doctoral student Pamela Bhatti presented the paper, which is co-authored by Wise and by research fellow Sangwoo Lee.